Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$130.35	13.617%	$148.0998	$148.10	$148.10	$148.10
Purchase #2	$93.60	10.338%	$103.2764	$103.28	$103.30	$103.30
Purchase #3	$59.73	10.821%	$66.1934	$66.19	$66.20	$66.20
Purchase #4	$55.27	8.734%	$60.0973	$60.10	$60.10	$60.10
Purchase #5	$57.81	12.683%	$65.142	$65.14	$65.15	$65.10
Purchase #6	$67.50	4.169%	$70.3141	$70.31	$70.30	$70.30
Purchase #7	$88.56	13.336%	$100.3704	$100.37	$100.35	$100.40
7 purchase totals =	$552.82		$613.4934	$613.49	$613.50	$613.50